ERROR while trying to add group 'psaadm'

[ecappa]

Hi all,
I am trying to update my Plesk (either via web interface and via cmd line autoinstaller), but at every beginning of the process I have the same error message ('of course it exists...'):

ERROR while trying to add group 'psaadm'

The detail of log file :

START plesk-base-9.3.0-fc4.build93100518.17 upgrading AT sam jun 12 07:46:13 CEST 2010
Create user 'psaadm' and group 'psaadm'
Checking for the group 'psaadm'...
Trying to add group 'psaadm'... groupadd: group psaadm exists

ERROR while trying to add group 'psaadm'

Aborting...

STOP plesk-base-9.3.0-fc4.build93100518.17 upgrading AT Sat Jun 12 07:46:13 CEST 2010

A bit of google search and a search here make me feel very alone...

Any idea ?

Thanks.